[CORed]

There are several possibilities: Some other program might be downloading it or creating and running it on the fly. The malware may have put a rootkit on your machine, which means that the malware has modified system program to make svhhost.exe invisible. Since you can see the file in Firefox, it seems likely that exporer has been modified to make the file invisible. Does it show up if you do "dir" in a command prompt? If so you might be able to delete it from the command prompt. You will probably have to kill it's process with the task manager in order to delete it, or delete it in safe mode.